Direct epoxidation of propylene to propylene oxide with molecular oxygen over Ag–Mo–W/ZrO2 catalysts

A series of Ag–(x)Mo–(5–x)W/ZrO2 (x = 5, 3.75, 2.50, 1.25, and 0) catalysts with different molybdenum content (x, wt%) were prepared by a slurry method. They were then applied to the direct epoxidation of propylene to propylene oxide with molecular oxygen. Selectivity for propylene oxide showed a volcano-shaped trend with respect to molybdenum content. This result was well correlated with the binding energy shift of Ag 3d5/2 of the catalysts. Among the catalysts, Ag–(3.75)Mo–(1.25)W/ZrO2 catalyst with the highest binding energy shift of Ag 3d5/2 showed the best catalytic performance. Furthermore, Ag–(3.75)Mo–(1.25)W/ZrO2 catalyst was reusable in the direct epoxidation of propylene.